Reinforced thermoplastic compositions of highly crystalline polyester resins have been described, inter alia, in U.S. Pat. Nos. 4,115,333; 4,125,571; 4,215,032 and 4,425,457. They exhibit considerable tendency to warp, and efforts to reduce warp by adding modifiers, tend to reduce surface appearance, as measured by gloss.
In U.S. Pat. No. 4,115,333, Phipps et al. disclose such reinforced compositions comprising a poly(1,4-butylene terephthalate) resin and a second resin of polycarbonate, glass fibers and a small amount of zinc stearate to improve warp resistance. Although the compositions in the '333 patent are eminently suitable for many uses as molded articles, good warp values as measured on a 4 inch.times.1/16 inch thick disk after 30 minutes at 350.degree. F. are only obtained when a second resin, polycarbonate is used. See, e.g., Example 2A. Gloss is not too good, either.
Scott et al., U.S. Pat. No. 4,125,571, describe thermoplastic molding compositions consisting essentially of a combination of polyesters, e.g., PBT and poly(1,4-cyclohexane -dimethanolterephthalate-co-isophthalate), and reinforcing filler of glass and mica. Good warp values are also obtained by Scott et al.'s molding compositions but these were subject to much greater variability with higher contents of glass and lower contents of PBT, i.e., replacement by poly(1,4-cyclohexanedimethanol terephthalate-co-isophthalate). Gloss was not as high as desirable, either.
In U.S. Pat. No. 4,215,032, Kobayashi et al. describe polyester compositions for molding materials composed of solid PET, an organic crystallization promoter, e.g., glycidyl ether of a polyalkylene glycol, and glass fibers. The PET compositions in this patent are not, however, particularly resistant to warpage under heat stress.
In U.S. Pat. No. 4,425,457, Christiansen et al. disclose PET resin compositions containing reinforcing filler of glass fibers and nucleating agents of monovalent metal salts. These compositions are not shown to have superior physical properties such as impact strength or resistance to warpage. Gloss was not optimum here either.
It would be useful to incorporate into these thermoplastic polyester materials a thermoplastic elastomer to impart high surface gloss and better resistance to warp. It would be helpful also to improve impact resistance, moldability, colorability, compatibility and the like. Resistance to warp is particularly critical when using high glass contents in thermoplastic compositions which, as the prior art has shown, tend to decrease such resistance.
Unexpectedly, it has now been discovered that such objects can be achieved by using an amorphous or semi-crystalline thermoplastic. These can be incorporated into reinforced PET or PET/PBT molding compositions so as to improve surface gloss and resistance to warp on exposure to heat, while at the same time imparting toughness and strength. Articles molded from such compositions are useful in many applications including under-hood automotive applications, electrical connectors, appliance bases and power tool housings.